The present invention relates generally to filters and, more particularly, to a reversibly expandable and collapsible pleated air filter element that can be inserted into a reusable filter frame.
Many conventional residential heating and cooling systems include a disposable filter. These filters typically include a frame, a filter material formed of glass fibers or similar material, and a mesh screen or the like that supports the filter material. After a period of use, these filters become dirty or clogged and must be replaced. This is accomplished by replacing the entire filter assembly with a new filter and discarding the old one. Depending on the use of the filter, replacement may be required several times a year. Because the frame and screen are discarded with the assembly even though it is only the filter material that is no longer functional, there is unnecessary waste and cost associated with such filters. In addition, because these filters are rather bulky, they are often purchased as they are needed rather than keeping a large supply on hand. Because purchasing a new filter is not always convenient, replacement can be delayed resulting in reduced efficiency of the system.
Filter assemblies with frames and removable filter elements are known in the prior art. U.S. Pat. No. 3,280,984 (Sexton et al.), for example, discloses a filter assembly comprising a support frame including upstream and downstream grid retaining panels and a flat pad of filter medium disposed in the frame.
U.S. Pat. No. 3,774,377 (Bishop) discloses a filter assembly with a replaceable filter element including a frame, a disposable and replaceable filter medium, and means for retaining the filter medium in a fixed position in the frame.
U.S. Pat. No. 3,789,589 (Delany et al.) discloses a filter assembly including a casing and a drawer arranged in the casing that contains pleated filter media. The drawer includes a plurality of comb-like assemblies having pointed fingers that are disposed in the pockets of the pleated filter media to prevent the filter from collapsing. The filter includes strips extending across each end portion of the downstream side of the filter so the side edges of the downstream folds will be equally spaced.
U.S. Pat. No. 4,042,358 (Frohmader) discloses an air filter formed into an accordion-shaped body having reverse folds forming pockets. The filter includes a string-like pleat spacing member that passes through a series of openings in the pleat walls. The spacing member is intended to equally space the pleats when the filter is in its expanded condition.
U.S. Pat. No. 5,840,094 (Osendorf et al.) discloses a filter assembly including first and second frame members, a filter element, and separate comb-like spacers for retaining the filter pleats in an open spaced manner.
U.S. Pat. No. 6,033,453 (Weddell, III) discloses a reusable frame support rack for supporting and retaining an outstretched, replaceable pleated media filter core. The frame includes a pair of longitudinal angles extending between a pair of transverse angles which carry a flat expanded metal support or reinforcement system.
There remains a need, however, for a collapsible pleated air filter having uniform spacing and cross web stability that can be quickly and easily expanded and inserted into a reusable filter frame.
It would therefore be desirable to provide a reversibly collapsible and expandable pleated air filter having uniform spacing and cross web stability when fully expanded and inserted into a reusable filter frame, but which can be collapsed for compact shipping, storage, and disposal.
The present invention provides a reversibly collapsible and expandable replaceable filter element for use with a reusable filter frame. The filter element includes pleated filter media and a flexible spacing structure attached to the media. The pleated filter media is reversibly collapsible and expandable and has an inlet side, an outlet side, opposed first and second ends, and an interior face region. The pleated media also includes fold lines each defining a pleat tip and a pair of adjacent panels. To limit the expansion of the filter element, the spacing structure is preferably inelastic.
In one embodiment, the spacing structure is arranged adjacent at least the interior face region of the filter media. By providing the spacing structure adjacent the interior face region, the spacing structure allows the filter media to expand only to a predetermined length corresponding to the length of a corresponding filter frame into which it is to be placed, and limits the degree of expansion of the center portion of the filter media, therefore preventing the filter media from being over expanded. In this embodiment, the spacing structure may be open and contain a plurality of openings that allow for air flow or it may have a closed structure that blocks or interferes with the flow of air through the filter element. If the spacing structure has a closed structure, it will be recognized that the size of the spacing structure must be minimized to minimize the impact of the spacing structure on the flow of air though the filter element, or the spacing structure must be located to minimize its interference with the air flow.
In one aspect, the spacing structure is attached only to the opposed first and second ends of the filter media. In another aspect, the spacing structure is attached over the entire surface of the filter media including the interior face region. In a preferred aspect, the spacing structure contains openings to allow air to flow readily through the structure. In a specific aspect, the spacing structure is an open mesh, net, scrim, screen, or the like containing a plurality of air flow openings, or at least one individual string arranged perpendicular to the pleats.
In one embodiment, the length of the spacing structure between successive pleat tips is less than two times the length of a panel measured from one pleat tip to the next alternating pleat tip so that when the filter element is in its fully expanded condition, the spacing structure forms a generally planar structure and adjacent panels form an angle of less than 180 degrees.
In one aspect of the invention, successive pleat tips define an attachment surface and the spacing structure is attached to the attachment surface. In one embodiment, the spacing structure is arranged along the inlet side of the filter media. In another embodiment, the filter element includes a second spacing structure arranged along the filter media outlet side.
In a more specific aspect, the length of the spacing structure between successive pleat tips is less than the length of a panel measured from one pleat tip to the next alternating pleat tip, whereby when the filter element is in its fully expanded condition, the spacing structure forms a generally planar structure and adjacent panels form an angle of less than 60 degrees.
In another aspect, the spacing structure is formed of a synthetic plastic material. The scrim may be provided in the form of at least one strip arranged perpendicular to the fold lines along the interior face region of the filter media. In a specific embodiment, the length of the spacing structure between successive pleat tips is equal, thereby providing uniform spacing of the pleat tips. In a more specific embodiment, the length of the spacing structure between successive pleat tips is at least 5 millimeters.
In another embodiment, the filter element includes attachment members along the opposed first and second ends of the filter media parallel to the fold lines for securing the filter element to the filter frame. In another aspect of the invention, the attachment members have a stiffness greater than the filter media stiffness.
In another embodiment, the present invention provides a replaceable filter element for use with a reusable filter frame including reversibly collapsible and expandable filter media and a flexible spacing structure containing a plurality of openings attached to the filter media. In this embodiment, the spacing structure can be attached to the opposed first and second ends of the filter media, can be attached to each successive pleat tip over the entire face of the filter media, can be attached to successive pleat tips along the edges of the filter media only, or can be attached to successive pleat tips in the interior face region of the filter media only.
The filter media can be either self-supporting or non self-supporting. If the filter media is non self-supporting, the spacing structure is preferably provided over the entire face of the filter media. If the filter media is self-supporting, the spacing structure may be provided over the entire face of the filter media or over only a portion of the face of the filter media including the interior face region of the filter media.